The present disclosure relates to a light emitting device and a manufacturing method for the same.
Light emitting devices using semiconductor light emitting elements such as LEDs (light emitting diodes) are widely used in various market segments, including backlights, lighting equipment, and automotive headlights. Light emitting devices using a blue LED and various phosphors such as green to yellow phosphors and red phosphors have been proposed to output white light having high color rendering quality. Several types of phosphors are commonly mixed into a sealing resin to be applied on the surface of an LED. If several types of phosphors are used in a mixture, however, yellowish green phosphors having larger specific gravity and particle diameters settle to the bottom first. Thus, the light emitted from yellowish green phosphors is readily absorbed by red phosphors. Red phosphors are also excited by the light from yellowish green phosphors and emit red light. Since the excitation of red phosphors takes place in two stages, the wavelength conversion efficiency is reduced from the standpoint of converting the wavelength of the blue light from a blue LED, which leads to a reduction of output of a white light source.
For example, Japanese patent publications 1-5, i.e., Japanese Unexamined Patent Application Publication Numbers 2007-184330, 2007-184326, 2009-182241, 2005-228996, and 2004-71726, disclose light emitting devices which employ a combination of a blue LED and various types of phosphors such as green and red phosphors. These patent publications propose light emitting devices constructed by disposing a red phosphor layer and a green phosphor layer in that order from the blue LED side so as to make it more difficult for the green light from the green phosphor to be absorbed by the red phosphor.
Moreover, Japanese patent publication 6, i.e., Japanese Unexamined Patent Application Publication Number 2011-243977, for example, proposes a light emitting device provided with a reflective film on the lower face side of the LED to increase the optical output from the upper face and the lateral faces thereof.